1. Field of the Invention
This invention relates generally to the field of semiconductor fabrication. More specifically, the invention relates to new precursors for the deposition of cobalt containing films onto substrates.
2. Background of the Invention
Cobalt silicides are compounds useful in the electronics field, particularly regarding the manufacture of integrated circuits and micro-electronics. Interest in cobalt silicides is increasing as device scale-down progresses due to their good thermal and chemical stability, low resistivity, wide process window and the small lattice mismatch to the silicon crystal lattice, which allows the cobalt silicide to be grown epitaxially on silicon.
ALD (Atomic Layer Deposition) and CVD (Chemical Vapor Deposition) are particularly useful techniques for deposition of metal and metal suicide films as compared to other methods of deposition such as physical vapor deposition (PVD) methods like sputtering, molecular beam epitaxy, and ion beam implantation. CVD may also be used to provide flexibility in the design and manufacturing of electronic devices, including the potential to reduce the number of processing phases required to provide a desired product.
ALD and CVD of various metals have been hampered by the lack of suitable precursor compounds. For example, conventional cobalt organometallic precursors, such as Co(acac)2, Co(acac)3 (acac: acetylacetonato ligand), CO2(CO)8, Co(C5H5)2(cobaltocene), Co(C5H5)(CO)2 and Co(CO)3(NO) have not demonstrated satisfactory properties for use in forming device-quality cobalt silicide films. Other precursors such as Co(acac)2 and Co(acac)3 have low vapor pressures and therefore require high temperatures to produce a vapor flow sufficient to support CVD or ALD. Carbonyl-containing molecules might be subject to decomposition, especially during light or heat exposure, which may lead to the evolution of the very harmful, toxic CO molecule. Phosphine-containing molecules are disqualified for the same reason. Organic phosphines are very hazardous and PF3 being both toxic and might lead to undesired phosphorus contamination and fluorine-induced etching/damage. Such chemicals might therefore be subject to strict regulations. For instance, CO2(CO)8 is volatile and can produce cobalt metal coatings without the addition of a reducing agent, but is too thermally unstable to be a practical CVD precursor, giving rise to competing side reactions and decomposition during storage, even under vacuum or an inert atmosphere. Likewise, Co(CO)3(NO) can be subject to unacceptable contamination with carbon and oxygen in the resulting cobalt and cobalt silicide layers when deposition is conducted at less than 350° C. or with a hydrogen flow of less than 500 standard cubic centimeters (sccm). Cobaltocene may be used to deposit cobalt films, but such films can be subject to severe carbon and oxygen contamination problems, even when hydrogen is used as a reducing agent.
Consequently there exists need for new cobalt suitable cobalt precursors for ALD and CVD applications.